Field of the Invention
Embodiments of the present invention concern the domain of rotors in rotating machines such as centrifugal compressors. More specifically, embodiments of the present invention relate to stacked rotor structures for axial compressors, pumps, axial or radial turbines, and electric motors including a plurality of wheels crossed by a central tie rod.
Description of the Related Art
A rotor may be made in different ways, in particular a rotor may include a single solid shaft on which elements, such as vane wheels, are assembled radially and locked using different means of transferring axial forces and torque.
A rotor may also include an axial stack of elements, such as vane wheels, assembled together using an axial preloading system, such as a central tie rod. The axial locking is provided by the preloading system, and the torque is then transmitted either by dry friction between the contact surfaces or using front cogging, such as in Hirth or Curvic couplings.
Embodiments of the present invention apply in particular to axial stacking rotors including a central tie rod arranged about the axis of the rotor.
There are axially stacked rotors including a central tie rod on which compressor wheels are mounted that is screwed at a first extremity into a first shaft end. The second extremity of the tie rod is inserted into a second shaft end and the second shaft end is bolted to one of the wheels. There are also axially stacked rotors including a tie rod passing through the second shaft end and attached using a nut. A hydraulic tool is then mounted onto the second extremity of the tie rod and it presses against the second shaft end in order to preload the tie rod.
However, such a configuration is complex and adds offset weight to the extremity of the rotor. Furthermore, the diameter of the central tie rod is dependent on the diameter of the shaft ends. Consequently, the load capacity cannot be increased. The length of the central tie rod in such configurations cannot be reduced.
In order to have a shorter central tie rod having a larger diameter, the second shaft end could be assembled using a bolting flange. However, such an assembly is more complex and prevents precise control of the preloading of the screw-tightened bolting flange.
Reference may also be made to document U.S. Pat. No. 3,749,516, which describes a stacked rotor comprising a central tie rod screwed at both extremities thereof into the two shaft ends. The tie rod is preloaded and centred by a central mechanical system, by screw tightening and/or by preheating the tie rod. Such a solution also prevents the preloading of the tie rod from being precisely controlled.
In view of the foregoing, the purpose of embodiments of the present invention is to overcome the drawbacks related to rotors having a central tie rod.